In recent years, circuit modules having a plurality of electronic components including semiconductor components and passive elements mounted on their wiring boards have rapidly spread. The circuit modules are employed for radio communications equipment such as cellular phones and have the functions of processing high-frequency signals.
In order to thus process the high-frequency signals, shielding layers having electromagnetic shielding functions are formed in the circuit modules such that unnecessary electromagnetic waves do not leak outward while restraining the effects of electromagnetic waves from the exterior. In such conventional circuit modules, metal covers have been most commonly used as the shielding layers.
In order to reduce the heights of the circuit modules, however, it is favorable to cover the electronic components with insulating resin materials. However, the insulating resin materials do not have the electromagnetic shielding functions. Therefore, the functions must be newly added to the insulating resin materials.
Therefore, circuit modules having shielding layers formed therein by sealing electronic components mounted on wiring boards with insulating resin materials and covering the insulating resin materials with conductive resins have been proposed (see, for example, Patent Document 1). The operations of the circuit modules can be stabilized by connecting the conductive resins to ground electrodes provided in the wiring boards.
Furthermore, the necessities of not only electromagnetic shielding from the exterior but also shielding electromagnetic waves between electronic components that are placed on wiring boards have arisen with recent higher frequencies.
When the electronic components including high-frequency power amplifiers are mounted on the wiring boards, for example, unnecessary electromagnetic waves generated from power amplifiers may adversely affect the other electronic components on the wiring boards. In order to shield the electromagnetic waves generated from the power amplifiers, therefore, configurations in which shielding plates are disposed between the electronic components including the power amplifiers and the other electronic components have been proposed (see, for example, Patent Document 2).
FIG. 30 is a cross-sectional view of a conventional circuit module having the above-mentioned shielding plate disposed therein. In such a conventional high-frequency module, a semiconductor component 102a including a power amplifier and the other electronic component 102b are arranged side by side on a wiring board 101, and are covered with a metal cover 103. Between the semiconductor component 102a and the other electronic component 102b, a shielding plate 105 made of a metal is formed so as to separate both the components. The shielding plate 105 has its upper end connected to a ceiling surface of the metal cover 103 and has its lower end connected to a ground electrode provided on the wiring board. This allows unnecessary electromagnetic waves from the semiconductor component 102a to be effectively shielded.    Patent Document 1: JP 2004-172176 A    Patent Document 2: JP 2002-185338 A